Rotating-field pulse transmitter



M y 1 5 D. B. PARKlNSON ,3

ROTATING-FIELD PULSE TRANSMITTER Filed March 13, 1950 3 Sheets-Sheet l 7I75 I77 1/ /3 I a! 5 [a FIG.

FIG. 2

lNl/ENTOR By D. B. PARK/NSON A TTORNEY y 19, 9 D. B. PARKINSON 2,639,332

RQTATI IGTIELD PULSE TRANSMITTER Filed March 13,1950 3 Sheets-Sheet 2INVENTOR D. B. PA RK INS ON A [TORNEV May 19, 1953 D. B. PARKINSONROTATING-FIELD PULSE TRANSMITTER Filed March 15, 1950 3 Sheets-Sheet 5INVENTOR D. 8. PA RK INS ON ATTORNEY Patented May 19, 1953 (Lift; 1''.

ROTATING-FIELD PULSE TRANSMITTER David B. Parkinson, Cleveland Heights,Ohio, assignor to Bell Telephone Laboratories, Incorporated, New York,N. Y., a corporation of New York Application March 13, 1950, Serial No.149,326

This invention relates to telephone calling or signalling circuits,apparatus and methods, and

more particularly to telephone calling methods, circuits and apparatusof the preset type which generate pulses of electric current fortransmission over voice frequency telephone channels to controlautomatic switching equipment for the establishment of communicationpaths between a calling subscriber and a called subscriber.

More particularly this invention relates to improvements in telephonesignaling methods, circuits and equipment of the type set 'forth in apatent application of Lovell-Parkinson Serial No. 35,926, filed June 29,1948, which issued as Patent 2,587,635 on March 4, 1952.

The system disclosed in that application employs a motor mechanism at asubscribers station which is actuated by power transmitted over thesubscriber's line.

An object of the present invention is to provide improved and simplifiedsignaling and calling methods, circuits and apparatus at a telephonesubscribers station for the transmitting of sim-' ilar types ofsignalling pulses in which a motor mechanism with a rotating or moving.armature is not required. Neither are any moving contacts required togenerate the signaling pulses, thus eliminating the cost of maintenanceof said mechanical devices as motors, contacts and the like.

In the above-identified application of Lovell Parkinson the subscribersstation is provided with a group of manually controlled switches ordials which the subscriber sets in accordance with the number or stationdesignation of the called subscriber. These finger wheels areinterconnected between two motor driven distributors in thatapplication, one operating at a relatively low speed to select aparticular number wheel or' digit and the other operating at arelatively high speed for generating pulses representing the digit to betransmitted.

A feature of the present invention relates to an improved arrangementfor generating the pulses operating at high speed and thus replacing thehigh-speed distributor of that application which results in improvedoperation and reduced main-' tenance costs of the subscribers stationset.

In the above-identified application and in the exemplary embodiment ofthe present invention of the digits or identity of the symbolscomprising the called station designation is represented by the timeelapsing between a reference or start 5 Claims. (01. ,179 90) I pulseand the stop or digit pulse. The pulse gen erating equipment is arrangedto generate two pulses for each digit of a called subscribersdesignation, the first pulse is usually called the start pulse and thesecond pulse a stop pulse. The two pulses representing one digit arefollowed by two pulses representing the succeeding digits and so on. Thepulses representing a complete'subscribers'design'ation are spaced fromother pulses representing another repetition of the same subscribersdesignation by means of a blank spacing interval during which no pulsesare transmitted; This blank orspacing interval is longer than theinterval between any of the pulses representing any of the digits,numbers or other information represented by the pulses.

In transmitting pulses of short duration over voicefrequencytransmission paths, difficulty is frequently encountered due totransients set up by the pulses. The transients are usually decayingalternating currents which are'caused by resonance circuits employed intelephone trans mission paths, repeat coils, filters and othertransmission equipment. Transients resulting from the application ofshort pulses to such equipment persist'for a number of cycles and thusfor an appreciable interval of time after the excitingpulse hasterminated.

In accordance with the present invention, the transmitting apparatus isarranged to space the signaling pulses transmitted so that ample timeisallowed for the transients associated with or appearing incident tothe application of each of the signaling pulses to the signaling ortransmis'-" sion system to die out sufficiently so that each transientwill not interfere with the next signaling pulse.

The manner in which the apparatus in ac-- cordance with the presentinvention may be incorporated in a complete telephone system isdisclosed in a copending application of W. A. Malthaner, Serial No.35,925, filed June 29, 1948, which issued as Patent 2,620,399 onDecember 2, 1952. Suitable types of equipment for responding to thesignaling pulses transmitted from apparatus disclosed herein aredisclosed in the copending applications of Vaughan, Serial No. 35,911,filed June 29, 1948, which issued as Patent 2,603,715 on July 15, 1952;Malthaner, Newby and Vaughan, Serial No. 68,234, filed December 30,1948, which issued as Patent 2,615,971 on October 28, 1952.

Novel features disclosed but not claimed herein are claimedin differentones of the above-identi-' fied patent applications or in the patentapplication of D. B. Parkinson, Serial No. 39.015, filed July 16, 1948,which issued as Patent 2,499,606 on March 7, 1950.

In accordance with an exemplary embodiment of the present invention aslow-speed distributor mechanism is provided which is driven by astepping mechanism which makes one step in response to each half cycleof arr applied alternating current. In addition, the signaling pulsesare generated during each half cycle of the ap plied alternating currentby a: pulse generator comprising means for producing a rotating magneticfield from polyphase alternating currents. These alternating currentsmay be'obtairied from power supplied over the subscribers line ortlrey'may be applied from an alternating-current power source local to asubscribers station, or supplied to the subscribersstation independentlyof the subscribers line. As shown in the drawing, the power is obtainedover the subscribers line: and the phase of. the various currents controlled by phase networks at the subscrib'ers station.

A plurality or saturable magnetic: members: are angularly disposed inthe rotating magnetic field.

Each of these saturabier magnetic members is provided with; a windingand the members are positioned in the magnetic. field? in accordancewith the time at which it is desired: to have a pulse generated in thewinding interlinising' the various saturable members. The pulses aregen:- erated in the windings surrounding these members at substantiallythe: time at'wl'iich the flux through. the member passes through zero,that: is,

when. it is changing most rapidly. At all other times during each cycieor halt? cycle of. the al' ten-rating current or during 'eaclr half:rotation of the: magnetic field these saturable members aresubstantially saturated. so that the flux through themdoes not changematerially.

Thus; during" each complete cycle or rotation of the magnetic field theflux goes through zero at two regular positions in the field. As aresuit, each coil will have two pulses induced in it" for each completecycle of the applied alternating current or rotation of the magneticfieldgassume ing of course, that the applied alternating cur-- rent isemployed to generate a two po'le mag.- netic field analogous to atwo-pole. induction motor. If the input windings which produce the magneticfield: are arranged to generate. more poles: in the field, then eachpair of poles; will in? duce two pulses in. each winding during eachcomplete rotation of the magnetic field; which: is again equivalent totwo pulses for each. cycleof the applied alternating: current.

In general, the presence of saturable magnetic elements may produce somesmall distortion in the magnetic field so that it may be necessary todetermine the exact position of these: elemerits experimentally tocompensate for suclidistortions. of the field as they may produce. Thuseleven such elements in all will be required. one for the start pulseand one for each of theten stop or digit pulses representing the digits0 to 9.. A. pulse is produced from. each of the coils during each halfcycle of the applied. alternating current.-

The foregoing and other objects and features of the invention will beapparent fromv the 101- lowing description, the novel features of whichare set forth in the appended claims, when read with reference to thedrawings, in which:

Fig. 1 is a front View partly broken away of the dialing or selectingapparatus;

Fig. 2 is a side view of the same apparatus;

Fig. 3 shows a section taken along line 3-3 of Fig. 1;

Fig. 4 shows the manner in which the finger wheels or dials, theslow-speed stepping mechanism, the rotating field pulse generator, andother apparatus are interconnected. to" cooperate one with another andwith a telephone transmission line for generating and transmitting the-de sired pulses representing a called subscribers designation;

Fig. 5 shows a top view of a suitable slow stepdevice;

6- is a; side view partially broken away of thestepping mechanism;

Fig. '7 is a front view partially broken away of the stepping mechanism;

Fig. 8 shows a section partially broken away taken along line 88 of Fig.6; and

Fig. 9 is a partial disclosure of the stepping mechanism showing thepole-pieces; the armature the stepping? pawls and; ratchet. wheels.

In the exemplary embodiment provision is made for the gen ration oipulse representationsof eight characters during each cycle of operation,these pulses arerepeatedly generated long as the alternating-currentsupply is connected to thegenerator and stepping switch. Any arbitrarilychosen number of representations of characters (within reasonable limitsmay be gen eratedby properly designed signaling apparatus. A maximum ofeight representations of charactors was selected for this disclosuresince eightcharacter calling numbers are in common use in telephonesystems. It will be understood that these characters may be digits orletters or a combination. or the two as commonly used in des ignating.telephone calls. Each of the digits 0 to 9 will be represented by adifferent combination' of two pulses; the pulse combination representingthe digitv 2 will also represent the letters A, B and. C; the pulsecombination representing the digit. will also represent the letters D. Eand F; and soon; Hereinafter-each combination of. eight characters willbe referred to as each called. number'irrespective of whether thecombination comprises digits or letters and digits.

In accordance with an. exemplary embodiment of this. invention. each of.the pulses generated is of about 1 millisecond in duration. When pulsesof this duration are transmitted over various types of. voice frequencycommunication paths encountered in telephonesystems, about 3%;milliseconds arerequired. for the longest transients to dieoutsufficiently so that the succeeding pulse may be accurately recognizedwithout interferonce from the transient caused by the previous pulse; Inother words, each. transmitted pulse of approximately l-millisecondduration is effect lengthened by a decaying alternating current ofapproximately Zita-millisecond duration. At the end of this 3-millisecond period or any time thereafter a second pulse may betransmitted.

The signaling system employed irrthe exemplary embodiment of theinvention set forth herein. generates a start pulse of aboutlinillisecond duration. for each character, the start pulses beinggenerated at M A-millisecond intervals as long as the power is supplied,and a stop pulse of about. l-millisecond duration for each character,each stop pulse starting during the 4- to 8 /2-milliseccnd interval oftime after the start of the start pulse. Inv order to provide suificientmargins of safety to permit reliable signaling, 4 milliseconds. areallowed. for the decay of each pulse and the-times of the start oftransmission assigned to stop pulses representing digits of'successivemagnitudes differ by millisecond. Thus, digit 1 is represented by astart pulse followed by a stop pulse which is initiated 4 millisecondsafter the start pulse was initiated, digit 2 is represented by a startpulse followed by a stop pulse which is initiated 4 milliseconds afterthe start pulse was initiated, and so on. It will be observed that thestop pulse for the digit 0 is initiated 8 milliseconds after its startpulse and 4 milliseconds before the next succeeding start pulse. Thus,there is required an increment of time of 4 milliseconds for thegeneration and decay of the start pulse, nine increments of time of /2millisecond each for the start of the generation of a pulse at any oneof the ten times necessary to represent the various digits, and a lastincrement of time of 4 milli-' seconds, all of the latter being requiredtopermit the stop pulse to decay only if it should occur at the end ofthe ninth increment of time. Consequently, 12 milliseconds of timeelapse between the start pulses of succeeding digits, from which itfollows that 12 milliseconds is required in this exemplary system totransmit each character designating the called number. In order toindicate the starting point of the transmission of a called number, atime interval of approximately-25 milliseconds is provided at thebeginning of the pulses representing a complete called number duringwhich no pulses are transmitted. Thus, 125 milliseconds of time arerequired to transmit the no-signal period and the pulse representationsof an eight-unit number.

As discussed hereinbefore, the apparatus dis. closed by this inventioncomprises a pulse generator, a stepping distributor and a selectorswitch which interconnects the pulse generator to the distributor sothat pulse representations of any eight-unit called number may beimpressed across the telephone line.

Figs. 1, 2 and 3 indicate one embodiment of the selector switch. It isenclosed in case I30, and selector dials II to I8 and release lever I33are accessible to an operator. The selector dials are made of anon-conducting material such as hard rubber or plastic, and each dial isprovided with ten indentations along its outer periphery. Eachindentation is designated by a letter or number or both, conforming tothe telephone signaling system, and each is'of suitable configuration topermit a persons finger to engage and move the dial. The selector dialsare separated by spacers I'II to I11, inclusive, which are attached tocase I30. As indicated in Fig. 3, each dial is attached to an individualsupport I00 so that each dial may be moved approximately one-fourth of arevolution about shaft 29. The inner surface of each dial is providedwith ten grooves which correspond to the finger indentations on theouter periphery of the dial. The grooves on each dial serve to en agewith a detent pawl to secure each dial in one of the ten possiblepositions as se-- lected by the operator. As indicated in Fig. 3, detentpawl 36 which cooperates with dial I6 is pivoted about shaft I 36.Spring 46 is attached between support I66 and pawl 36 sothat pawl 36 isnormally forced against dial I6, thereby securing the dial in a fixedposition by engaging with one of the ten grooves. Spring 46 also servest apply a continuous force to support I66 which tends to rotate supportI 36 and dial It in a clockwise direction about shaft 29. The grooves onthe dials and the detent pawls are shaped and positioned'so that bypressing upon the finger in- 6. dentations on the dials an operator canmove the dial in either direction and so that the ratchet action of thepawl against the grooves secures the dial in any of the ten positions towhich it may be moved. The rotary movement of the dials is limited toabout one-fourth of a revolution by stop I3I and insulator I9I.

Release arm I38 is connected with release lever I33 through lever I34(Fig. 2) and is provided with slots to engage each detent pawl. Whenlever I33 is in its normal position, arm I38 permits each detent pawl toengage with a groove in the corresponding dial. When lever I33 isdepressed, arm I36 is moved in a clockwise direction about shaft I 36and the detent pawls are disengaged from the dials, thereby permittingthev spring associated with each dial to cause each dial to return toits initial position.

A spring contact is connetcted to each dial, and each dial and springcontact may be moved so that the spring contacts may be connected withany one of ten conductors. As indicated in Fig. 3, spring contact 28 isattached to dial I6 and it is electrically connected to terminal I46through conductor 56. Insulator IQI supports the various terminals andconductors, and the ten conductors 5| to I0 whichmay be contacted byspring contacts 2| to 28 are mounted thereon;

The contact members 2| through 28 are connected to commutator segments9| to 98 and conductors 8| to 'II) are connected to the windingsinterlinliing the saturable members 335 and 3I0 through 3I9 as indicatedin Fig. 4 wherein selector switch I30 is indicated in schematic form.

In addition to the dials or manual selecting wheels and switchesrepresented by I30 in Fig. 4,

a slow-speed stepping mechanism is represented by brush arm II3,distributor segments 9| through 98, inclusive, and H5, ratchet wheel205, and pawls 208 and 209 which are attached to armature 2H] which inturn is actuated by the winding ZII.

The pulse generating equipment is shown schematically in Fig. 4connected to the subscribers line I25 through the manually controlledselecting mechanism I30 and the stepping mechanism comprising brush armH3 and stepping magnet 2| I, as wellas the ratchet wheel 2G6 and pawls208 and 209.

As shown in Fig. 4, the magnetic structure comprises an outer shell orring 30I and an inner ring or pole-piece 302. The magnetic field isgenerated radially across the space between these pole-pieces by meansof two windings 303 and 304 which windings are supplied with differentphases from a polyphase source of alternating start pulse coil 305 andten stop pulse coil struc-' tures 350 through inclusive, are alsoprovided. saturable material such as iron-nickel alloys or othersuitable ferromagnetic material. These saturable magnetic elements, asshown on the drawing, are angularly disposed in the radial magneticrotating field so that the zero of the field will pass these elements atsuccessively different intervals of time, thus generating pulses Thesestructures are made of readily in the windings inter-linking thesemembers at successively difierent intervals or" time. The outputs of thecoils are connected to the bus-bars of the manually controlled dials,finger wheels, or selector switch I38.

Figs. 5, 6, '7, 8 and 9 show one embodiment of a suitable type ofstepping device or switch and distributor. The distributor comprises adoubleended brush arm [13 moving over contacts 9! through 98 and H4. Thebrush H3 is driven by ratchet wheel 296 both of which are mounted uponshaft 201. The ratchet wheel 2% is driven by stepping pawls 208 and 299which are attached to a vibrating magnetic reed 2 It. The magneticstructure is polarized by permanent magnet 2I2 so the magnetic reed 2H1vibrates vertically as viewed in Figs. 6, '7, 8 and 9 in response toalternating current flowing in the coil 2| l surrounding the reed. Whenalternating current is applied to coil 2 the magnetic polarity of reed2! is changed each half cycle of the alternating cur rent so that thereed moves upward and downward during each cycle. Each time reed 2H3moves upward or downward carrying pawls 293 and 209, ratchet wheel 286is moved one step by each of the stepping pawls. Thus the ratchet wheel2% and brush [l3 are moved one step for each half cycle of the appliedalternating current.

In the embodiment shown in Fig. 4, the alternating current forenergizing the stepping magnet 2H is obtained from the voltage appearingbetween the center point of the simplex coils 292 and ground. Thiscurrent is in turn obtained from the power source connected between theconductors [25 of the subscribers line and ground by means of a simplexcircuit connection. As a result, the selector switch or slow-steppingdistributor takes one step for each half cycle of the alternatingcurrent. When desired, the tuning of the magnetic reed 210 may beadjusted so that the stepping magnet advances the ratchet wheel 286 nearthe beginning of each half cycle preceding the generation of a startpulse. Thus the switch is not stepped at a time which woul. interferewith the proper generation of the pulses relating to each of the digitsor symbols representing the subscribers number.

Of course, the time of advancing of the ratchet wheel 206 maybe adjustedeither before or after the start pulse so long as the switch does notadvance during any of the pulses and if compensating adjustments aremade at the receiving end of the subscribers line !25. When desired, thevarious times of advancing or stepping of the stepping switch relativeto the time other equipment is actuated may be adjusted by means ofelectrical networks instead of mechanical adjustments on the reed andstepping pawls.

In operating the subscribers station set, the subscriber will positionthe dials or finger wheels ll' through l8 and thus the spring or contactdevices 2! through 28 in accordance with the number or other designationin the called subscribers station. As a result, the contact membars 2!through 28 will make contact with the selected ones of the bus-bars 6!through 1D, inclusive, which extend to the magnetic type reed contactdevices H through 80, inclusive.

After the subscriber has thus set his station equipment, he willinitiate a call which, in turn, sets apparatus into operation in thecentral station, and as a result alternating current is applied to thesubscribers line.

As shown in the drawing, the source of alterhating current is'suppliedfrom the central sta' tion or some distant point over both lines of thesubscribers line in parallel by means of simplex coils 2G0. A similarsimplex coil or coils 202 is provided at the subscribers station and thealternating current thus obtained from the center point of these coilsand ground. Two phasesplitting networks, 203 and 204, are provided forobtaining two-phase alternating current from the power supplied from thedistant point over the subscribers line I25. The outputs of these phasenetworks are connected to the respective coils 303 and 3M and produce arotating magnetic field as described above in the usual andwellunderstood manner. Of course, when it. is so desired, the source ofpolyphase alternating current may be obtained locally at thesubscriber's station if available.

Assume for purposes of illustration that upon the application of thealternating current to the subscribers line I25 brush arm H3 willadvance one step from the position shown in the drawing. Due to theadjustments of the stepping device and the rotating magnetic fieldwithin the core structure, shown in Fig. 4 after the brush arm H3advances, a star pulse is generated in the coil 305 due to the directionof the flux reversing at this time. At this time a circuit extends fromthe lower conductor of line I25, the winding of coil 3%, stepping switchor distributor segment Hi, dist ibutor brush H3, segment 9|, contactspring 2!, one of the bus-bars 6| through 10 and the winding of one ofthe coils 3 I 0 to 3!!! to the upper conductor of the subscribers lineI25. As a resuit, a start pulse is transmitted over the subscribers lineI25 21. short interval of time after the brush arm H3 advances tosegment 9!. As pointed out above, the exact time of relationship betweenthe generation of the startpulse and the advancing of the brush arm H3may be controlled by the tuning and adjustmentof the stepping mechanism2l0, by the positioning of the start coil 385 relative to the energizingwindings 3G3 and 304 and also by means of any desired types of phasingnetworks comprising any suitable circuit elements.

During the remainder of this half cycle a pulse is generated; in each ofthe digit or stop pulse coils 3 It through 3G9, inclusive. The exacttime of the generation of the stop pulses is determined by the locationof the coils and their saturable cores in the rotating magnetic field isdescribed above. The pulses are generated in each of these coils whenthe flux reverses through the cores, in other words, at substantiallythe time the zero of the magnetic field passes the core, a pulse isgenerated in the windings of these coils. As pointed out above, some oneof the coils will be connected through the spring contact 2! at thistime. As a result. the particular coil. for example coil 3H, isconnected due to the spring contact 2i, associated with the first dialof finger wheel H, resting on bus-bar 51'. Under the assumed conditionsthe sto pulse will be transmitted during the seventh stop pulse intervalindicating a digit value of seven. This value may represent thenumerical digit 7 or it may represent a corresponding letter of thealphabet in accordance with the usual telephone dial stationdesignations.

It should be noted that a pulse is generated in each of the coils 305 3l 0 through 3 19. during each half cycle. However, as pointed, outabove, only one pulse is transmitted, namely, from coil 311 305, thecircuit will be completed from a lower conductor-ofline 125 through thecoil'305 and distributor segment H4, brush arm H3 and distributorsegment 92 at this time to contact member 22 which likewise ispositioned in engagement with one of the bus-bars 6i through by thecorresponding finger wheel I2 designating the second character or digitof the called subscribers number or designation. During the remainder 0fthe half cycle a stop pulse is again generated in each one of the digitor stop pulse coils 3l0 through 3H3, inclusive, and one of these will betransmitted, depending upon the position of the contact 22. It should benoted that at this time the pulses generated in all of the coils 305 andam through 319 will be of opposite polarity to the pulses generatedduring the first half cycle because the flux changes in the oppositedirection through each of these coils thus generating a pulse ofopposite polarity. In other words, the start pulse and the stop pulserepresenting any digit are of the same polarity but the start pulse andstop pulse representing a succeeding digit are of the opposite polarityto the pulses representing a preceding digit.

The above-described mode of operation then continues for thetransmission of pulses representing each of the digits or characters inthe called subscribers number or station designation. Under the assumedconditions the above-described cycle of operation will be repeated forthe transmission of eight characters, one for each of eight half cyclesor four complete cycles resulting in the transmission of a start pulseand a stop pulse representing each of the denominal orders of thesubscribers number or symbol place of a designation. After the completenumber has been transmitted, i. e., eight digits under the assumedconditions, brush arm I I3 passes off seg- .ment 9B and also off ofsegment H4 and remains ofi all segments for two half cycles or onecomplete' cycle of the applied alternating current. Thus, during thisinterval no pulses are transmitted which indicates to the equipment atthe central ofilce that pulses of one complete designation have beentransmitted and that the following pulses transmitted will represent thevarious digital values of the subscribers number transmitted thereafter.At the end of this silent interval or pause, the above-describedoperations are repeated during which two pulses representing each of thedigits or symbols of a called sub-- scribers station designation ornumber are again transmitted.

The above-described mode of operation then continues for thetransmission of all the ini'ormation required at the switching centers.After suificient pulses have been transmitted to control the equipmentat all the switching centers necessary to establish a transmission pathfrom the calling subscriber to the called subscriber, operation of thetransmitting equipment, described herein, at the subscribers station isinterrupted by removing the source of alternating current from the lineand other equipment provided at the central station as well as at thesubscribers 10 station'is actuated to establish a path'to-th'e calledsubscribers station.

Numerous modifications of theabove-described exemplary embodiment ofthepresent invention will occur to people skilled in the art withoutdeparting'from the spirit of the invention as so forth-in the claimsappendedhereto.

. What is. claimed is:

1. In combination in a telephone. signaling system,apparatusforgenerating a plurality .of pulses comprising a subscribersline, means for receiving alternating-current power from said line,phase adjusting networks for obtaining polyphase currents from saidalternating current power, apparatus for generating a radial rotatingmagnetic field from said polyphase currents, a plurality of saturablemagnetic elements radially disposed within said magnetic field, awinding surrounding each of said magnetic elements having a pulsegenerated therein as the zero of the rotating magnetic field passes theposition of the respective magnetic elements, and switchmeans forconnecting said winding to said line for transmitting said pulses oversaid line.

2. In combination in a telephone subscribers station set, a subscribersline connected thereto, means for receiving alternating currents fromsaid line including phase control means for obtaining a plurality ofdifferent phases of alternating current, apparatus for obtaining aradial rotating magnetic field from said alternating currents, aplurality of saturable magnetic ele ments disposed in said field andsaturated thereby, windings individual to each of said magnetic elementshaving pulses generated therein as the direction of flux through saidsaturable elements changes due to the rotation of said magnetic held, amanually controlled selector switch connected to said windings forselecting certain of said windings and a stepping distributor connectedbetween said selecting switch and said subscribers line for successivelyconnecting selected ones of said windings to said subscribers line.

3. In a telephone calling system, a subscribers line, apparatusresponsive to alternating current received over said line for generatingpolyphase alternating currents therefrom, means for producing a rotatingmagnetic field from said polyphase alternating currents, a plurality ofsaturable magnetic elements, windings individual to and each linked withits respective one of said elements, positioning means for positioningsaid elements radially in said field at selected positions in accordancewith the time for a generation of pulses in the respective windings andswitch means for selectively connecting said windings to saidsubscribers line for transmission of pulses thereover.

4. In combination in a telephone signaling device, pulse generatingapparatus comprising a core structure, a plurality of polyphase windingsWound upon said core structure, a connection for applying polyphasealternating currents to said windings for producing a radial rotatingmagnetic field by said core structure and windings, a plurality ofsaturable magnetic elements radially disposed within said magneticfield, a winding surrounding each of said magnetic elements having apulse generated therein as the zero of said rotating magnetic fieldpasses the position of the respective magnetic element.

5. In a telephone calling system, a subscriber's line, apparatusresponsive to alternating current received over said line for generatingpolyphase 11' 1'2 alternating currents therefrom, means for protivelyconnecting said windings to said sub u in a t n m e i fi l f m Said P yscribers line for transmitting pulses from said phase alternatingcurrents, a plurality of satucoils over said line. rable magneticelements, windings individual to DAVID B. PARKINSON, and each linkedwith its respective one of said 5 elements, positioning means forpositioning said References Cited in the file of this P te t elementsradially in said field at selected positions UNITED STATES PATENTS forgenerating pulses within said windings at Number Name Date the time atwhich the field reverses through said 2'499i606 Parkinson fin-n Mar. 7'1950 saturable elements and switch means for seleco

